The present invention is directed to coating methods and chemical coating compositions in general, and more particularly to improved methods for increasing the effective contact area of electrodes during electrocoating of a non-conductive workpiece which has been coated with an electroconductive primer.
In the prior art, coating methods have been devised for applying certain chemical coating compositions to non-metallic workpieces. In some instances, it has been desirable for such non-metallic workpieces to be coated in such a way to match the coatings disposed on metallic workpieces. Where electrocoating has been utilized for thesemetallic workpieces, it has been very difficult to obtain suitable color, gloss and texture matching, as well as good adhesion, chip resistance, ultra-violet light resistance, flexibility and other durability characteristics for the non-metallic workpiece.
One proposal for alleviating the problems and difficulties associated with these particular coating applications has been the development and utilization of electroconductive primer compositions which may be applied to a non-metallic workpiece, such as a polymeric workpiece. These electroconductive primers have then permitted the simultaneous electrocoating of both the non-metallic and metallic components of a combined, or composite, workpiece.
Preferred embodiments of these electrocoating methods have been developed and pioneered by the W. C. Richards Company of Blue Island, Ill. and are disclosed and claimed in patent application Ser. No. 922,318, filed on Oct. 23, 1986, entitled "Improved Conductive Primer Compositions and Methods", the disclosure and teaching of which are incorporated herein by reference.
However, one particular difficulty associated with such improved electrocoating methods has been the phenomenon of "burn-out" in areas of the electroconductive primer located adjacent to the coating electrodes. Such "burn-out" has been caused by the utilization of the necessary large electrical voltages in order to effectuate electrocoating for such large workpieces as composite automobile bumpers, large automotive panels, etc.
One suggested method of solving the "burn-out" problem has been to increase the effective area of the electrode contact by placing a metallic, and hence conductive, sheeting in contact with both the electrocoating electrode and a relatively large expanse of the electroconductive primer coated workpiece to be electrocoated. One such attempt has involved the use of aluminum foil spread over a relatively large area of the electroconductively primed workpiece immediately adjacent to the electrocoating electrode. However, these techniques have proved to involve difficulty of application, uniformity of result, problems in repeatability and inaccuracy of results, inter alia.
Accordingly, it has been a material object of the improved electrocoating methods and compositions of the present invention to materially alleviate the above difficulties and deficiencies of the prior art.
It has been a further material object of the improved electrocoating methods and compositions of the present invention to provide an increase in the effective area of the electrocoating electrode, while at the same time providing for accuracy and repeatability of results, as well as uniformity and ease of application.
It is yet further an object of the improved electrocoating methods and compositions of the present invention to provide methods utilizing highly electroconductive compositions which will form an intimate contact with electroconductive primers to facilitate the electrocoating process without experiencing the prior phenomenon of "burn-out".
It is yet further a material object of the improved electrocoating methods and compositions of the present invention to provide electroconductive coating compositions in a greater electro-conductivity than the electroconductive primer compositions per se, thereby further to facilitate the electrocoating process.
These and other material objects of the improved electrocoating methods and compositions of the present invention will become apparent to those of ordinary skill in the art upon a review of the following summary of the invention, brief description of the drawing, detailed description of preferred embodiments, the appended claims, and the accompanying drawings.